1. Field of the Invention
The invention relates to a driving circuit of a liquid crystal display and its relating driving method, and more particularly, to a driving circuit with its gamma adjustable and having a lookup table (LUT), and its relating driving method.
2. Description of the Prior Art
A liquid crystal display (LCD) has advantages of lightweight, low power consumption, and low divergence and is applied to various portable equipment such as notebook computers and personal digital assistants (PDAs). In addition, LCD monitors and LCD televisions are gaining in popularity as a substitute for traditional cathode ray tube (CRT) monitors and televisions. However, an LCD does have some disadvantages. Because of the limitations of physical characteristics, the liquid crystal molecules need to be twisted and rearranged when changing input data, which can cause the images to be delayed. For satisfying the rapid switching requirements of multimedia equipment, improving the response speed of liquid crystal is desired.
Please refer to FIG. 1, which is a timing diagram of the pixel voltage and the transmission rate V1 according to a prior art LCD. In FIG. 1, the pixel voltage is shown with the straight lines, and the transmission rate V1 is shown with a dotted line. In FIG. 1, frame N means a frame period, and frame N+1, N+2 . . . mean the following frame periods. Due to the physical characteristics of liquid crystal molecules, when the pixel voltage is switched from a data voltage C1 to a data voltage C2, the liquid crystal molecules cannot be twisted to a predetermined angle within a single frame period, resulting in failure to perform at a predetermined transmission rate. As the curve of the transmission rate V1 shows, the transmission rate V1 cannot reach a predetermined transmission rate until the frame period of frame N+2. The delayed response-time will cause blurring on the LCD.
An over-driving method is utilized to improve the response-time. Please refer to FIG. 2, which is a timing diagram of the pixel voltage and the transmission rate V2 according to a prior art LCD using an over-driving method. When the pixel voltage is switched from the data voltage C1 to the data voltage C2, an over-driving data voltage C3 is added to accelerate the response speed of the liquid crystal molecules. Since a higher data voltage can obtain a faster response speed of the liquid crystal molecules, a data voltage C3 that is higher than the data voltage C2 can improve the response-time enough to reach the predetermined transmission rate in a single frame period. As FIG. 2 shows, the curve of the transmission rate V2 reaches the predetermined transmission rate in frame N.
The U.S. published application No. 2002/0050965 discloses an over-driving method using a brief table to store the over-driving image data. The brief table only includes part of the over-driving image data for driving the pixels switched from one gray scale to another. When the driving circuit receives the image data from the input terminal, a processor is used to perform an interpolation operation to expand the brief table. Hence, an extra algorithm is needed in the conventional over-driving method. The effect of using an extra algorithm is that it will slow down the response speed.
In addition, there is no description relating to the adjustment of gamma of an LCD. In the prior art, the overdrive and adjustment of gamma depend respectively on two different circuits, which complicates the whole circuit.